Abstract

The responsivity of an extreme-ultraviolet transmission grating
spectrometer with silicon photodiode detectors was measured with
synchrotron radiation. The spectrometer was designed to record the
absolute radiation flux in a wavelength bandpass centered at 30
nm. The transmission grating had a period of 200 nm and relatively
high efficiencies in the +1 and the -1 diffraction orders that were
dispersed on either side of the zero-order beam. Three photodiodes
were positioned to measure the signals in the zero order and in the +1
and -1 orders. The photodiodes had aluminum overcoatings that
passed the desired wavelength bandpass centered at 30 nm and attenuated
higher-order radiation and wavelengths longer than approximately 80
nm. The spectrometer’s responsivity, the ratio of the photodiode
current to the incident radiation power, was determined as a
function of the incident wavelength and the angle of the spectrometer
with respect to the incident radiation beam. The spectrometer’s
responsivity was consistent with the product of the photodiode
responsivity and the grating efficiency, both of which were separately
measured while removed from the spectrometer.

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